With less than a half-second to liftoff, Space X's Flacon 9 rocket launch to the International Space Station was aborted Saturday because of high pressure in an engine.

The center engine pressure built above limits and a shutdown occurred one-half second before liftoff, SpaceX officials said.

The next launch attempt could come as early as Tuesday, but that determination won't be made until the engine itself is inspected, said Gwynne Shotwell, president of SpaceX. There also is a launch window May 23.

"We had a nominal ignition for all nine (engines)," Shotwell said. "Engine 5 started fine and (its chamber pressure) started trending high."

She said the high pressure could be the result of high temperatures possibly from too little fuel flowing into the engine, though it is too early to know for sure. "We're going to have to spend more time looking at the data."

The rocket was poised on Space Launch Complex-40 at Cape Canaveral Air Force Station, Fla., for the attempt. Its hangar is next to the launch pad. Shotwell said the company is prepared to take the engine out of the rocket if needed to and replace it with an engine already at the Cape.

The goal of the mission is to launch a SpaceX Dragon capsule to the International Space Station to demonstrate cargo delivery using privately built spacecraft. It will be a landmark event because no privately constructed spacecraft has docked with the orbiting laboratory.

NASA is working closely with SpaceX under the provisions of the Commercial Orbital Transportation Services contract.

"We're ready to support when SpaceX is ready to go," said Alan Lindenmoyer, NASA's manager of the Commercial Crew and Cargo Program.

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